Hard gelatin capsules which may be used for packaging pharmaceutical medications are well known. Not so well known, however, are the difficulties which must be overcome to properly manufacture these capsules. For example, when literally thousands of capsules are manufactured each hour by a single machine, it is not suprising that a great amount of care must be taken to insure there is some degree of uniformity between capsules of the final product. Indeed, this is no small problem. Using presently available apparatus, the variation in weight of these capsules can be as much as thirty percent.
As is well known, typical procedures for manufacturing hard gelatin capsules involve momentarily submerging capsule mold pins in a relatively large liquid gelatin bath and then withdrawing the coated pins from the bath. The gelatin on the pins is then allowed to dry and the cast gelatin is subsequently removed from the mold pin to become an upper or lower half of a gelatin capsule. The efficacy of mold pins, however, is dependent on heat transfer between the pin and the gelatin bath. This is where presently available gelatin molding machines have some problems.
First, it is to be appreciated that before insertion of the mold pins into the gelatin bath, there is a temperature differential between the mold pins and the bath which is approximately between twenty-one and thirty-six degrees centigrade (21.degree.-36.degree. C.). This is so because the gelatin bath is typically maintained in a temperature range between forty-five to sixty degrees centigrade (45.degree.-60.degree. C.) whereas the mold pins are at room temperature, e.g. twenty four degrees centigrade (24.degree. C.). This temperature differential is important as it promotes effective coating of the mold pin by the liquid gelatin. It also, however, affects the depth of the coating. Thus, for uniformity in coating, it is desirable there be consistently equivalent temperature differentials between each mold pin and the liquid gelatin bath into which it is dipped. Furthermore, this temperature differential should be constant and substantially equal not only for all of the mold pins which are simultaneously coated in one dip, it should remain so from dip to subsequent dip.
With presently available gelatin capsule molding devices, liquid gelatin is typically held in a dish having one large single well. Many mold pins, i.e. perhaps as many as one hundred fifty (150) or more, are simultaneously dipped into this well during each operational cycle. Consequently, due to the temperature differential and the resultant transfer of heat from the liquid gelatin bath to these mold pins, "cold spots" will remain in the gelatin bath when the pins are withdrawn. Unless these "cold spots" are effectively removed from the bath of liquid gelatin prior to the dipping of the next group of mold pins, the temperature differential between the mold pins and the liquid gelatin bath will have changed. Although a pumping mechanism may be used to move the gelatin within the bath to disperse these "cold spots", the largeness of the bath makes effective dispersal nearly impossible. One consequence of this will be that subsequently dipped mold pins will experience a different coating action which varies the film thickness of their coatings from those of previously dipped mold pins. This should be avoided.
The present invention recognizes that by using a plurality of smaller wells, rather than one large well, the liquid gelatin in each well can be completely replaced between dipping operations. The present invention also recognizes that a multi-well tray which is submerged in a bath of liquid gelatin can be used to establish a plurality of fluid passageways through which the gelatin can be moved to effectively disperse the "cold spots" which result from a mold dipping operation.
Accordingly, it is an object of the present invention to provide an apparatus for manufacturing hard gelatin capsules which uses a multi-well tray that effectively disperses the "cold spots" which occur when the mold pins are dipped into the gelatin bath. Another object of the present invention is to provide an apparatus for the manufacture of hard gelatin capsules which continuously influences a general pattern of gelatin flow to prevent the creation of eddies and fluid flow stagnation points that can adversely affect the coating of the mold pins with gelatin. Another object of the present invention is to provide an apparatus for the manufacture of hard gelatin capsules which maintains the entire gelatin bath at a substantially constant temperature by continuously circulating and mixing the gelatin. A further object of the present invention is to provide an apparatus for the manufacture of hard gelatin capsules having a plurality of wells in which the gelatin temperature in any well is substantially equal to the gelatin temperature in each of the other wells in order to equally coat all capsule forming mold pins to create uniformly thick capsules.